Dragline buckets are commonly used as an effective means of excavating overburden and winning coal during surface mining operations. Examples of common types of prior art dragline buckets can be found in U.S. Pat. Nos. 5,575,092 to Smit, 5,307,571 and 4,944,102, both to Behlendorf et al., as well as in now expired U.S. Pat. Nos. 2,584,416 to Boehringer and 1,908,686 to Burke. Each of these dragline buckets generally include a front, or forward, ring-like portion having a plurality of teeth for digging into the ground and a rear, basket-like portion for holding the excavated materials. Typically, the two components are joined to form a unitary bucket using welds, rivets, or other substantially permanent joining techniques. This creates a long lasting, durable bond that ensures that the unitary bucket can withstand the rigors of the excavation process without the components detaching from each other.
While a dragline bucket of unitary construction is effective for its intended purpose, it does suffer from one very significant shortcoming. Specifically, in a dragline bucket of unitary construction, it is difficult to separate the forward ring from the basket in the event that damage occurs to either component during extensive excavation operations, or if one of the components fulfills its useful life prior to the exhaustion of the full service life of the opposite component. In the past, extensive metalworking processes, such as cutting welds or removing a plurality of rivets, have been required to separate the components. It should be appreciated that such operations are very labor intensive and time consuming. This is particularly evident when one considers the size of a typical dragline bucket which has a capacity on the order of 220 cubic yards or more. In many situations, this can lead to significant production downtime for the dragline operation.
Another difficulty with prior art buckets is that the forward ring and basket are commonly made of very thick and heavy sections of durable metal materials, such as steel. Of course, the goal in using such materials is to prolong the service life of the individual components. This is a primary concern when one considers the previously described difficulty encountered when repairing and maintaining a bucket of unitary construction. The use of heavy metal materials, however, is not without its deletarious side effects.
Specifically, these materials greatly increase the weight of the bucket. Of course, the greater the weight of the bucket, the less the weight of material that may be removed by a dragline of given power (i.e. a larger portion of the lifting capacity of the dragline is used to lift the bucket and as a consequence there is less capacity available for lifting material).
If the basket could be easily replaced, it would be possible to use thinner and/or lighter construction materials since component service life would not be the primary design consideration it is at present. When lighter materials are used in the construction of the bucket, a larger portion of the lifting capacity of the dragline is available to lift material won during the mining operation. As such, more material may be won in each pass of the bucket and overall mining efficiency may be greatly enhanced.
Thus, a need is identified for a dragline bucket that overcomes the above-described limitations of the prior art. The bucket would have a basket that is secured to a forward ring in a manner that allows for easy removal and replacement. In addition to improving the efficiency of the repair operation, the simplicity and ease of replacement would permit the use of thinner materials of less overall weight in fabricating the basket. Overall, the improved dragline bucket would result in a significant improvement over baskets formed as a unitary whole using welding, rivets, or other permanent joining techniques.